The imaging apparatus in the past converts into a digital signal an electrical signal photoelectrically converted and outputted by an image pickup device such as a CCD (Charge Coupled Device) and performs digital signal processing so as to obtain a predetermined picture signal. Furthermore, the imaging apparatus having a zoom function can generally shoot by arbitrarily determining an angle of view from a wide-angle side to a telescopic side by using an optical zoom lens before the image pickup device. And it can further obtain the picture signal on the telescopic side by an electronic zoom process for electrically expanding an object image formed in a central portion of the image pickup device by the digital signal processing.
FIG. 9 is a block diagram showing an overview configuration of the imaging apparatus having the zoom function in the past.
In FIG. 9, an imaging apparatus 30 is the imaging apparatus which has the zoom function by means of an optical zoom and an electronic zoom and generates a television signal and so on from an output signal of the image pickup device so as to output it. A lens 40 forms the object image on an image pickup device 42. A motor 41 is the motor for driving the lens 40. The image pickup device 42 is the image pickup device for photoelectrically converting the CCD and so on. A TG (Timing Generator) 43 is a timing generator for driving the image pickup device 42. An AD converter 44 is an AD (Analog to Digital) conversion circuit for converting the output signal of the image pickup device 42 into the digital signal. A signal processing portion 45 is a signal processing circuit for performing a color separation process, a gamma process and so on based on the output signal of the AD converter 44 and generating a luminance signal and a color-difference signal.
Zoom operation buttons 46 are buttons for a user to perform a zoom operation. In general, the zoom operation buttons 46 are comprised of an expansion button (or a TELE button) for expanding an image and a reduction button (or a WIDE button) for returning an expanded image to its original state. A zoom switching portion 47 is a circuit for determining whether an expansion/reduction process according to the operation of the zoom operation buttons 46 should be performed by the optical zoom or electronic zoom and switching between them. An optical zoom control portion 48 is the circuit for outputting a control signal for controlling the motor 41 to perform the expansion and reduction process by adjusting the angle of view of the object formed for the image pickup device 42 by the lens 40 based on the determination of the zoom switching portion 47.
In the case where the lens 40 is on the most telescopic side (TELE terminal), the optical zoom control portion 48 outputs a notice signal for notifying it to the zoom switching portion 47. The zoom switching portion 47 switches between the optical zoom and electronic zoom based on the notice signal and the operation of the zoom operation buttons 46.
Here, a switching process of the zoom switching portion 47 will be further described.
FIG. 10 is a diagram showing the switching process between the optical zoom and electronic zoom by the zoom switching portion 47 of the imaging apparatus 30 in the past. As shown in FIG. 10, the zoom switching portion 47 switches to the electronic zoom after the lens 40 to be moved by the optical zoom reaches the TELE terminal. To be more precise, an optical zoom control portion 48 detects the TELE terminal of the optical zoom from a position of the motor 41, and outputs the notice signal to the zoom switching portion 47.
Next, the operation of the above-mentioned image pickup device in the past shown in FIG. 9 will be described by taking as an example the image pickup device comprised of 480 pixels by 720 pixels shown in FIG. 11A.
FIG. 11A is a diagram showing an example of pixel mixture of the image pickup device in the past.
Usually, the image pickup device 42 performs interlace reading when shooting a moving image. To be more specific, charges of two vertically adjacent pixels are mixed and transferred to the image pickup device 42 by a drive from the TG 43. As shown in FIG. 11A, the image pickup device 42 forming a color filter of a complementary color for each pixel outputs a signal having mixed the charges of two pixels of cyan (Cy) and magenta (Mg) and a signal having mixed the charges of two pixels of yellow (Ye) and green (Gr).
As above, the image pickup device 42 mixes two pixels in a vertical direction, and outputs the signal by vertical 240 pixels and horizontal 720 pixels as an equivalent of one field. Next, this signal is converted into the digital signal by the AD converter 44. Next, the color separation process, gamma process, and luminance signal and color-difference signal generation are performed by the signal processing portion 45. It is also possible to generate and output an NTSC television signal based on the luminance signal and color-difference signal.
Next, the process of the electronic zoom of the imaging apparatus in the past will be described.
FIG. 11B is a diagram showing a method of reading the charges from the image pickup device in the case of performing the electronic zoom process. As shown in FIG. 11B, in the electronic zoom process in which an output is produced by electrically expanding a part of a screen, an expanding process is performed by using the signal in the central portion of the image pickup device 42. FIG. 11B is the case of performing the electronic zoom of 2× scaling factor (processing scaling factor), where the 240 pixels in the central portion, of the vertical 480 pixels, are read by taking one field period. To be more specific, the signal in the central portion of the image pickup device 42 is intermittently read by one horizontal line so that the signal is extended to one field period (one image scanning period) and outputted.
On intermittent reading, during the period in which the signal is not read from the image pickup device 42, the signal processing portion 45 performs an interpolation process by using a memory and so on for interpolating by utilizing the signal already read. Therefore, the signal to be read by the electronic zoom process in the case of the electronic zoom of 2 times shown in FIG. 11B is the signal of 120 pixels in the vertical direction as to the image pickup device 42. The signal processing portion 45 generates the signal of 240 pixels in the vertical direction, by means of the interpolation process by using the memory, from the intermittently read signal of 120 pixels in the vertical direction.
However, the above-mentioned imaging apparatus uses the image pickup device for reading data of the same number of pixels as a resolution of a display device such as a TV monitor, and so, in the case of the electronic zoom process of which scaling factor is 2 times for instance, a ¼ portion of an imaging surface of the image pickup device is displayed on the entire surface of the display device. Thus, there is a problem that the resolution of the image displayed on the display device becomes ½ horizontally and vertically.
To be more specific, in the case where the image pickup device comprised of 480 pixels by 720 pixels is utilized to expand it by the electronic zoom process to 2 times in the horizontal and vertical directions respectively, the vertical 480 pixels and horizontal 720 pixels are generated by interpolating based on the signal of vertical 240 pixels and horizontal 360 pixels (¼ of the number of all the pixels) in the central portion of the image pickup device so that the resolution is significantly reduced.
In recent years, the image pickup devices as well as the pixels are miniaturized due to miniaturization of semiconductors. For that reason, there are increasing numbers of the imaging apparatuses for shooting the moving images using the image pickup device having the number of pixels equal to or more than the number of moving image recording pixels, which can also be used for shooting the static images, in addition to shooting the moving images, by utilizing multiple pixels thereof.
As will be explained by referring to FIG. 15, the embodiments including this embodiment and the following embodiments will be described on the assumption that the image pickup device of a line of horizontal 2160 pixels and vertical 1440 pixels is used as shown in FIG. 16.
In FIG. 15, reference numeral 1400 denotes a lens for shooting, 1401 denotes a diaphragm apparatus for controlling an amount of light passing through the lens 1400, 1402 denotes a CCD image pickup device for converting a formed optical image into the electrical signal, 1403 denotes a gain control amplifier capable of changing an amplification factor at appropriate times, 1404 denotes an A/D converter for converting an analog signal into the digital signal, 1405 denotes a signal processing circuit for converting an imaging signal into the data for recording, 1407 denotes a timing generator for supplying an operation timing signal to each portion, 1408 denotes a controller for controlling each of the above described, and 1409 denotes a reduction processing circuit for converting an image size of an inputted image signal.
The optical image having passed through the lens 1400 and diaphragm 1401 is converted into the electrical signal by the CCD image pickup device 1402. The imaging signal obtained from the CCD image pickup device 1402 is preprocessed in an analog fashion by the gain control amplifier 1403, sampled by the A/D converter 1404, processed into a record image signal by the signal processing circuit 1405, recorded on a record medium through the reduction processing circuit 1409 to have the number of pixels in compliance with a record format on shooting the moving image thereafter, and sent to the record medium with the as-is number of pixels on recording the static image. Each portion is controlled by the control signal from the controller 1408, and the timing generator 1407 supplies an appropriate timing signal to each portion based on it.
At this time, the signal from a necessary pixel must be read at a frame rate (approximately 1/60 second in the case of NTSC) in order to record the moving image. In that case, if driven to read the signal from the entire multi-pixel image pickup device, it becomes a very high-speed reading clock so as to cause a problem such as reduction in transfer efficiency of the charges of the image pickup device.
In the case of reading the image pickup device of a line of horizontal 2160 pixels and vertical 1440 pixels at 60 frames, reading speed is 2160×1440×60=187 MHz so that the transfer efficiency of the charges of the image pickup device is conspicuously reduced. It is possible, on shooting the static image, to sufficiently reduce the reading speed since it is not restrained by the frame rate.
However, the number of pixels to be recorded is originally smaller than all the pixels of the multi-pixel device, and so it is often rendered possible, in the case of an ordinary imaging apparatus utilizing the multi-pixel device, to drive it to cut out and selectively read only pixel signals necessary for the moving image from the multi-pixel image pickup device so as to operate and read at the same speed as driving the image pickup device of the ordinary number of pixels.
As in FIGS. 17A and 17B, on shooting the static image, the image pickup device is driven to read all the pixels as in FIG. 17A. At this time, it is driven at the speed sufficiently capable of reading since it is not restrained by the frame rate. On shooting the moving image, it becomes sufficiently feasible to read it to the extent not to reduce the transfer efficiency by reading only the lines necessary for the record format from the central portion of the image pickup device as in FIG. 17B.
By this method, however, the angle of view of the image shot through the lens of the same focal length is significantly different between the static image and moving image as understandable from FIGS. 17A and 17B.
In this connection, there is a known method of solving the above described problem by vertically adding and reading a plurality of pixels on shooting the moving image.
As will be explained by referring to FIG. 18, in the case of the image pickup device of vertical 1440 lines, an equivalent of three lines of vertical transfer CCD is added on the vertical transfer CCD and is vertically read as an addition signal of the three lines. The number of vertical read lines thereby relatively becomes 480 lines and a ⅓ vertical transfer rate becomes sufficient, and so the transfer efficiency is not reduced even if full-frame reading is performed so as to allow the transfer of the charges.
A circuit configuration in this case is in FIG. 19. Function of the reference numerals are the same as those in FIG. 15.
Furthermore, there is a devised system wherein, by utilizing this method and adding an electronic zoom circuit 1906 for expanding and reducing the signal obtained from a signal processing circuit 1905 as the circuit in FIG. 20, the method of adding three lines and reading from the entire screen, method of adding two lines and further cutting out and reading from the lines doubling the number of record lines (480×2=960 lines), and method of cutting out and reading only the number of record lines (480 lines) without adding the lines as in FIG. 21 are switched and the above described electronic zoom circuit 1906 is combined therewith so as to allow the electronic zoom of high scaling factor with little degradation of the image.
The operation of the controller for setting the electronic zoom circuit at this time is as in FIG. 22. The electronic zoom scaling factor is set at 1 time on ordinary shooting, where three vertical lines are added and the scaling factor of the electronic zoom circuit 1906 is 1 time. And in the case of operating the electronic zoom, the signal for adding three lines is used while the electronic zoom scaling factor is set between 1 and 1.5 times, and an electronic zoom scaling factor setting is sequentially assigned to the scaling factor of the electronic zoom circuit 1906 in a following stage to expand it.
Expansion is further continued, and when the electronic zoom scaling factor setting reaches 1.5 times, two vertical lines are added and the electronic zoom scaling factor setting divided by 1.5 is assigned to the scaling factor setting of the electronic zoom circuit 1906.
The expansion is further continued, and when the electronic zoom scaling factor setting reaches 3 times, vertical line addition is stopped and one line is read, and the electronic zoom scaling factor setting divided by 3 is assigned to the scaling factor setting of the electronic zoom circuit 1906.
However, as for the above described electronic zoom operation in the cases of adding three lines, adding two lines and only the equivalent of one line without performing addition, there will be significant differences, as a matter of course, in an signal charge amount per pixel out of the image pickup device, such as the “equivalent of the charges of three pixels,” “equivalent of the charges of two pixels” and “equivalent of the charge of one pixel” respectively.
For that reason, while performing the electronic zoom, brightness of the screen changes on switching the number of added lines so that it becomes an unnatural screen. Even if a diaphragm 1900 for exposure control is changed in order to prevent this, the speed of the diaphragm to follow cannot be so high, and so the brightness of the screen inevitably becomes discontinuous for a certain period of time.